A ten center study in seven countries y the World Health Organization has shown that weekly IM injections of 200 mg of testosterone enanthate provide extremely effective male contraception with minimum side effects. With less than one pregnancy per 100 person-years the injections compared well with injectable female contraceptives, and better than condoms, female oral contraceptives, or IUD's. The major problem with the method is user dislike of the large weekly injections, which proved to be the primary cause of dropout from the study. In Phase I BIOTEK has shown that injectable biodegradable microcapsules containing 68.3% testosterone base raises the testosterone level in female rabbits and maintains that level above 10 ng/ml for at least 75 days. During Phase II the best Phase i formulation will be optimized, scaled up, fully characterized, and subjected to stability testing. Additional animal studies will be conducted, an IND will be submitted to the FDA, and Phase II will conclude with a human clinical trial of safety and pharmacokinetics. The results of Phase II will then be used to solicit private-sector funding for a Phase III commercialization process. PROPOSED COMMERCIAL APPLICATION: If a sustained injectable dose form for testosterone were developed for contraceptive use, it would also be useful for the treatment of hypogonadism, since biweekly parenteral administration of testosterone is at present the preferred form of androgen replacement therapy. The injections are perceived as a source of frequent discomfort, and the field of androgen replacement therapy would therefore benefit directly from the contraceptive work proposed here.